CORE LAB ONLY - SAMPLE PROCESSING. This trial is a study with parallel questions to be evaluated. The overarching rational for ACTG 372 is to explore relevant questions while examining new treatment options for enrollees who have been receiving ZDV (or d4T) +3TC+IDV and are currently exhibiting a range of virologic responses. By dividing the study into the corresponding, non-sequential cohorts, different approaches to evaluating virologic success and virologic failure can be explored while maintaining long-term follow-up of subjects. Providing rollover options for all subjects on a particular regimen in an ACTG trial, irrespective of response, is a desirable goal as new approaches to managing response and failure can be pursued in parallel and in an efficient manner.